When planning and setting up wind power installations, the visual detractions to be expected on the part of the wind power installation on the environment play an increasingly important part in approval and acceptance. If for example a wind power installation is placed in the proximity of a residence, it is possible, when the sun is in unfavorable positions, that the wind power installation or the rotor thereof is between the sun and the residence. If the sunshine is not affected by cloud, the rotating rotor constantly throws a (strobing) shadow on to the property. The shadow casting caused by the wind power installation on the adjoining properties is often perceived by the residents as being very troublesome. Even if the wind power installation satisfies the legal approval requirements there is however not always any guarantee that the undesired shadow casting effect is prevented.
DE 199 29 970 A1 discloses a shadow casting regulating system in which the intensity of light is detected in order to derive therefrom whether a shadow can occur at all.
It will be noted however that an adequate level of light intensity is only one of the prerequisites for a shadow to occur. A further prerequisite is for example clear air. Under hazy visual conditions, the light is diffused so that only slight or no shadowing occurs, in spite of the high level of light intensity. Control of a wind power installation, which is based on the intensity of the light, can result in a shutdown although there is no shadow.